Caution: Don't date... him

They form Britain's least wanted list: an online database of men that womankind has declared are to be avoided at all costs.

Cads, lotharios and bedhopping chancers all take their place on a new website set up by cheated partners intent on sending out a warning to women around the world.

And just four months after dontdatehimgirl.com was launched, more than 20,000 Britons have joined up, either to post details of the bad behaviour of an ex-boyfriend or to check up on the past of a current one.

For thousands of men that has meant an unenviable starring role on the internet. Underneath their pictures is a series of scathing complaints, allegations and tirades.

The site, which is inspired by the FBI's "most wanted" list, contains an ever-expanding database of adulterers and heartbreakers, in the hope of stopping them duping any more unsuspecting female victims.

On the list is Mark from London. Apparently, he is not the sensitive single man he says he is. In fact, the 31-year-old has managed to cheat on his girlfriend of seven years with no less than 30 different women - including her best friend, the site claims.

"This guy is very good- looking and can be charming but is essentially the most selfish man in the world," says the report from one of his many spurned lovers. "To say he doesn't grasp the concept of faithfulness is an understatement. He is an awful man who lacks any respect for women and wantonly hurts them."

Begun in the United States, the site has already snared dozens of untrustworthy British lotharios. One young British woman who felt aggrieved enough to post a former lover on Dontdatehimgirl.com was Alex Butterworth, 24, from Bradford.

Last year Ms Butterworth, a police officer, began seeing a man who seemed perfect. He was tall, handsome and told her he was a professional rugby league player, on the books of Leeds Rhinos.

"I thought it was going really well, but obviously it wasn't - because he had a girlfriend," she said. "He was just telling more and more lies. Another time he said he couldn't see me because he was going out with his mate, but then I went out and bumped into that mate. It turns out he'd been with his girlfriend for two years."

But the worst revelation was yet to come. "He was very tall - about 6ft 5ins - and I believed he was in the Leeds Rhinos team. But then I did some detective work and looked on their website, and it turned out that he wasn't in the squad at all. The man in question had been lying about his age. He was in fact 17 and still at school.

"I'd just come out of a very complicated relationship and just wanted something easy-going but this just got worse and worse." She said she'd put him on the site because other girls - including his girlfriend - should be aware of what he was like.

"I believe very much in karma. What goes around comes around," she said. "He is definitely someone that girls in the Bradford and Leeds area should be aware of."

Dontdatehimgirl.com was founded by Tasha Joseph, 33, who has now given up her job as a Miami-based publicist to run the website full-time. "Men have been cheating since the dawn of time. Something like this is long overdue," said Ms Joseph.

"I'm really happy we thought of it. It's going to help women all over the world. It's about creating a sisterhood on the internet over the shared experience of infidelity."

Ms Joseph came up with the idea when a dinner conversation with friends, at a restaurant on Miami's South Beach last summer, turned to the infidelities of previous boyfriends.

"We just thought it would be a good idea to find out if a man was a cheater or a liar before investing time in him, perhaps by searching a large database along the lines of the FBI's most wanted."

That conversation, and the subsequent setting-up of the site, brought back painful personal memories for Ms Joseph, who had previously had her own heart broken by two cheating, former partners.

"The first time was when I was at college. I came home to find my boyfriend in bed with someone else," she said. "The other time, I had been with a guy for about a year, and another girl rang me to tell me he had been cheating with her. I was devastated, but also very, very angry. I guess that's how most women who post to the site feel."

The site has already infuriated and embarrassed countless men, including one who has gone to the lengths of setting up his own web site, www.classaction-dontdatehimgirl.com, to solicit fellow "victims" to press for a lawsuit against the women.

"We get threats every day, but nobody has actually filed a lawsuit," said Ms Joseph. "I'm not saying women can't find good guys and get in great relationships. I definitely have hope for that, but I think that while you're looking it's very good to have a resource like this."

Some of Britain's leading dating experts weren't so sure, though, warning that sites like dontdatehimgirl could simply provide a forum for bitter exes to vent their spleens.

Lorraine Adams, a dating agency director credited with bringing speed dating to the UK, said: "It's almost like meeting someone and putting a private detective on them before you fall for them.

"You also run the risk, with anything like this, of sour grapes. It's very difficult for a guy to finish with a girl; often she can get very hurt and offended. Maybe he's a normal man but there just wasn't the right chemistry. To her, he could be a despicable guy - the worst person on Earth. We all have different opinions of what is acceptable behaviour and what isn't."

Darren Richards, chief executive and co-founder of DatingDirect.com, the UK's largest internet dating site, said: "The theory is good. It's how eBay was built; people give feedback on users. But you have to remember that there are always two sides to every story - particularly where relationships are concerned."

Accepting this maxim, Ms Joseph is planning to launch another website later this month - Dontdateherman.com.